JP6159472B2 - Circuit apparatus and method for controlling piezoelectric transformer - Google Patents

Description

  The present invention relates to a circuit device and method for controlling a piezoelectric transformer.

  A piezoelectric transformer is also called a piezoelectric transformer, but is an electromechanical system that functions as a resonant transformer. The piezoelectric transformer can convert the supplied AC voltage into a higher or lower AC voltage. This conversion is performed at the resonance frequency of the piezoelectric transformer, which is determined by the mechanical size and material of the piezoelectric transformer.

  In a closed loop control method of a certain piezoelectric transformer, an input voltage, an input current, and a phase position thereof are used as closed loop control information. Based on these parameters, the piezoelectric transformer can be controlled and the closed loop control of its behavior can be performed. However, this does not result in an optimum operating point for the piezoelectric transformer. Losses that appear due to the effects of non-tunable closed loop control adversely affect the performance and efficiency of the piezoelectric transformer. This reactive power is prepared by the supply unit and is converted by the piezoelectric transformer only on the primary side.

  The objective is to detect the appropriate setting parameters for closed-loop control of the piezoelectric transformer, thereby optimizing the operation with minimal losses in the selected application area or field of the piezoelectric transformer at the selected application conditions. Is to guarantee. The operation of the piezoelectric transformer should be possible within the desired frame, whether pulsed or continuous. By utilizing appropriate feedback parameters, it should be ensured that the operating state of the piezoelectric transformer remains equal.

  For the operation of the piezoelectric transformer, in order to ensure the function of the piezoelectric transformer, in all operating states (starting, operation, load change, environmental condition change) It is necessary to provide the operating voltage and the operating current at the corresponding phase positions.

  This object is achieved by a circuit arrangement having the features of claim 1. The circuit device includes a first branch circuit including a piezoelectric transformer having an input capacitance, a second branch circuit that compensates the input capacitance, a first input coupled to the first branch circuit, and a second branch circuit. And a differential amplifier with a coupled second input.

This coupling can be effected by direct coupling or via a further part.
This circuit device uses a closed-loop control parameter that exists to express the behavior of a piezoelectric transformer with positive phase and positive amplitude, and enables excitation of vibration of the piezoelectric transformer with low loss.

  The input capacitance of the piezoelectric transformer is a capacitance according to the configuration between the piezoelectric transformer electrodes. The behavior of this piezoelectric transformer can be represented by an equivalent circuit diagram. An equivalent circuit diagram of a piezoelectric transformer including a series oscillation circuit including a capacitive element, an inductive element, and a resistor considers an input capacitance as a capacitive element connected in parallel to the series oscillation circuit. The current and voltage parameters representing the behavior of this series oscillation circuit are not directly accessible because of the parallel input capacitance.

  In one configuration, the first branch circuit has a series connection of a piezoelectric transformer and a first resistor. The second branch circuit has a series connection of a capacitive element and a second resistor. The second branch circuit is constructed in the same manner as the series connection of the input capacitor and the first resistor.

  The series connection of the capacitor and the resistor is a high pass filter. Since the high-pass filter in the first and second branch circuits is symmetric, the input capacitance can be compensated. This is because the capacitance element of the first branch circuit and the second resistor are connected in series. This time constant is equal to or approximately equal to the time constant of the series connection of the input capacitance of the second branch circuit and the first resistor.

  In one configuration, the piezoelectric transformer is in the first branch circuit between the first potential point and the second potential point, and the first resistor is in the first branch circuit, the second potential point and the third potential point. It is between the potential points. The capacitive element is located between the first potential point and the second potential point in the second branch circuit, and the second resistor is located between the second potential point and the third potential point in the second branch circuit. between. In this configuration, the second potential point in the first branch circuit is coupled to the first input, and the second potential point of the second branch circuit is coupled to the second input.

  Because the time constants are equal, the signal in the high-pass filter does not depend on the frequency and amplitude of the control unit, but occurs at the same amplitude and phase position. In view of these together, both signals appear at the input of the differential amplifier as a common-mode voltage, so that these signals are filtered by the differential amplifier, so that the signal component of the input capacitance of the piezoelectric transformer is filtered Is applied.

  The signal thus obtained is fed back in a closed circuit and becomes the basis for controlling the piezoelectric transformer. For this purpose, the output of the differential amplifier is coupled to a piezoelectric transformer via a feedback branch circuit. Advantageously, a feedback signal is applied to the first potential point of the first and second branch circuit, so that the third potential point to which the input electrode of the piezoelectric transformer is applied is a reference potential (which is ground and This may result in a parallel connection of high-pass filters.

  In one configuration, an additional amplifier is provided in the feedback branch circuit, which may provide a control voltage for the piezoelectric transformer. In the feedback branch circuit, an amplitude closed loop control can be provided, which is connected upstream from the further amplifier described above.

  In one configuration, the output of the differential amplifier is coupled to a piezoelectric transformer via a pulse width modulator and two switching elements connected in series between two potential points. The switching element is controlled by a pulse width signal, which is achieved by one of the switches being connected in conduction with an adjacent reference potential according to the pulse width signal. A control voltage for the piezoelectric transformer is detected between the switching elements. This apparatus amplifies a square wave pulse width signal.

  If advantageous, the circuit arrangement has a voltage closed loop control circuit that returns the signal at the output of the differential amplifier and a current closed loop control circuit that returns the current through the piezoelectric transformer, so that the detection The measured current and voltage are taken into account in the control. The returned signal is compared with the target signal. The control of the piezoelectric transformer is changed according to this comparison.

  The corresponding method is to control a piezoelectric transformer that is in the first branch circuit and has an input capacitance, but this method is between the first branch circuit and the second branch circuit that compensates the input capacitance. Detecting a voltage difference and feeding back to the piezoelectric transformer in a feedback closed circuit. Of course, further components can be provided in this closed circuit.

  In this method, the first branch circuit has a series connection of a piezoelectric transformer and a first resistor, a potential is detected between the piezoelectric transformer and the first resistor, and the second branch circuit is A capacitive element and a second resistor are connected in series, and a potential is detected between the capacitive element and the second resistor. At this time, the time constant of the series connection between the capacitive element of the second branch circuit and the second resistor is equal to or substantially equal to the time constant of the series connection from the input capacitance of the first branch circuit and the first resistor. .

  Hereinafter, the present invention will be described based on embodiments with reference to the drawings.

It is the schematic of the control circuit for piezoelectric transformers. It is a circuit diagram of the circuit device which controls a piezoelectric transformer. It is a circuit block diagram of a differential amplifier. FIG. 6 is a circuit diagram of a further circuit device for controlling the piezoelectric transformer. It is a circuit diagram of another circuit device which controls a piezoelectric transformer.

  FIG. 1 is a schematic diagram of a control circuit for the piezoelectric transformer PT. In the following embodiment, first, a basic consideration for controlling the piezoelectric transformer PT in the control circuit will be clarified. In this control circuit, two amplifiers 100 and 200 are connected in a closed circuit, The piezoelectric transformer PT is employed as a series element.

  The behavior of the piezoelectric transformer PT controlled by this type of circuit device is explained by a simplified equivalent circuit diagram (ESB), which is the geometric size of the piezoelectric transformer PT, as well as the dielectric and elasticity of the material. And the piezoelectric material constant. The components of the equivalent circuit diagram can be determined within the frame of impedance measurement, for example.

  This equivalent circuit diagram includes a lossy series oscillation circuit 6 including a capacitive element Cs, an inductive element Ls, and a resistor Rs. A capacitive element Cp is connected in parallel to the series oscillation circuit 6, and this corresponds to the input capacitance of the piezoelectric transformer PT. This input capacitance Cp is a parasitic capacitance according to the configuration and significantly affects the (external) total current.

  Excitation of the piezoelectric transformer PT at a resonance frequency can be performed using a linear amplifier 100 that performs self-excited vibration and is fed back. In order to excite the series resonant frequency or the parallel resonant frequency, the piezoelectric transformer PT is controlled by the linear amplifier 200 with a small output resistance. Overcurrent occurs in the piezoelectric transformer PT during resonance. The current through the piezoelectric transformer PT can be displayed as a voltage through a resistor (not shown in FIG. 1) that functions as a shunt, and can therefore be supplied to the input of the excitation amplifier. .

  Thereby, the phase condition for exciting to the resonance frequency is satisfied even when there is a limit based on the influence of the input capacitance Cp. The amplitude condition in practice requires an amplification factor that is slightly larger than is necessary to compensate for the loss in the piezoelectric transformer PT. This type of excitation circuit with two amplifiers is referred to in the literature as a “Butler” circuit.

  Due to the input capacitance Cp, the current required for feedback is not available for direct detection by the series oscillation circuit 6. However, a circuit for compensating for the influence of the input capacitance Cp is required to generate a feedback signal that passes for the excitation circuit.

  FIG. 2 is a circuit diagram of a circuit device for controlling a piezoelectric transformer PT having this type of compensation.

  This circuit device includes a first branch circuit 1 having a series connection of a piezoelectric transformer PT and a first resistor R, and a second branch circuit 2 having a series connection of a capacitive element Ck and a second resistor Rk. Have The second branch circuit 2 functions to compensate for the influence of the input capacitance Cp of the piezoelectric transformer PT.

  The piezoelectric transformer PT is between the first potential point 11 and the second potential point 12 of the first branch circuit 1, and the first resistor R is the second potential point 12 and the third potential of the first branch circuit 1. Between point 13. The third potential point 13 is also a reference potential and can also be referred to as ground. The capacitive element Ck is located between the first potential point 21 and the second potential point 22 in the second branch circuit 2, and the second resistor Ck is connected to the second potential point 22 in the second branch circuit 2 and the second potential point 22. Between the three potential points 23. The third potential point 23 is at the reference potential. The first and second branch circuits 1 and 2 are connected in parallel.

  Further, the circuit device includes a differential amplifier 3 having a first input 31, an inverting second input 32, and an output 33. The first input 31 is connected to the second potential point 12 in the first branch 1. The second input 32 is connected to the second potential point 22 in the second branch 2. Alternatively, the potential points 12, 22 can be coupled to the inputs 31, 32 via additional components. The differential amplifier 3 amplifies the difference between the input signals here and provides a corresponding signal on the output side. In an ideal differential amplifier with optimal common-mode blocking, the output voltage depends only on the voltage difference and not on the absolute value of the voltages applied to both.

  The circuit device further has an amplitude closed-loop control unit 4 that changes the amplitude of the signal on the input side. When the amplitude is relaxed, it is also referred to as an amplitude limiter. In embodiments of the amplitude closed loop controller 4, there may be linear or non-linear signal effects. The input 41 of the amplitude closed loop control unit 4 is connected to the output 33 of the differential amplifier 3.

  Furthermore, this circuit arrangement has a further amplifier 5, which amplifies the input signal Ue by a factor V0. An input 51 of the amplifier 5 is connected to an output 42 of the amplitude closed loop control unit 4. The output 52 of the amplifier 5 is connected to the first potential points 11 and 21 of the first and second branch circuits 1 and 2, and as a result, the output voltage Ua of the amplifier 5 passes through the first branch circuit 1. Is also applied via the second branch circuit 2. Alternatively, the output 52 of the amplifier 5 can be coupled to the first potential points 11, 21 via further components.

  The input capacitor Cp and the first resistor R functioning as a shunt resistor or a shunt resistor form a high-pass filter, and the capacitive element Ck of the second branch circuit 2 acting as a compensation branch unit; Similarly to the second resistor Rk, a high-pass filter is formed. The component sizes of components Ck, Rk, R have the same time constant τ = RC (ie, τ = R × Cp to τ = Rk × Ck), so both are the same Selected to have a critical frequency. The inputs 31 and 32 of the differential amplifier 3 do not depend on the frequency and amplitude of the closed loop control unit, and the signal from the second branch circuit 2 and the signal from the high-pass filter of the first branch circuit 1 are the same. It appears to have an amplitude and a phase position. A prerequisite for this is that the input capacitance Cp does not depend on the amplitude of the applied voltage.

  Considering both of these, both of these signals are generated as an in-phase voltage on the input side of the differential amplifier 3 and are suppressed by the differential amplifier. As a result, only the signal magnitude of the series oscillation circuit 6 is amplified. Is done. Under ideal conditions, the differential amplifier 3 provides a positive phase feedback signal corresponding at least approximately to the equivalent circuit diagram of the piezoelectric transformer PT.

  FIG. 3 shows one circuit configuration (test circuit) of the differential amplifier 3, which differs from the circuit configuration presented in FIG. 2 in the following points.

  Resistors R1 are connected between the first input 31 and the second input 32 of the differential amplifier 3 and the second potential nodes 12 and 22, respectively. Furthermore, a further resistor R2 is connected between the first input 31 and the reference potential. A further resistor R2 is also connected between the second input 32 and the output 33. By selecting the resistance values of R1 and R2, an amplification factor that depends on the quotient of these resistance values can be set. It should be noted that the circuit diagram shown can be part of an amplifier closed circuit as presented in FIG.

  In this type of closed circuit, after applying the supply voltage Ua, oscillation is heard as a result of electrical noise in the closed feedback closed circuit. A prerequisite is the presence of a linear amplifier with sufficient bandwidth, at least for small signals, in addition to the phase-amplitude condition. The amplifier does not cause an additional phase shift unless it is desirable for closed loop control purposes. If the amplitude is higher, there is a non-linearity in the sense of amplitude limitation, which may be desired. Amplitude limiting is also possible at the amplifier input. FIG. 2 shows an amplitude limit 4 on the output side of the differential amplifier 3.

  By inserting the amplitude closed loop controller 4 into the feedback branch circuit, it is possible to keep the exciter signal in a sinusoidal curve, so that harmonics are avoided. This kind of amplitude closed-loop control can be performed through measurement of the current amplitude, comparison with the target value, and subsequent changes in the amplification factor of the feedback closed circuit. This device oscillates within the bandwidth of the amplifier at a frequency such that the piezoelectric transformer PT has the highest grade, ie the highest closed circuit amplification. If this frequency is not the desired operating frequency, a bandpass filter (not shown) may be installed in the feedback closed circuit. This selectively suppresses unnecessary resonance that is possible.

The concept described above can be applied to various variations or types of control circuits.
FIG. 4 is a schematic circuit diagram of an alternative circuit device for controlling a piezoelectric transformer.

  This circuit device has a piezoelectric transformer PT in the measurement circuit, and a current I of this piezoelectric transformer flows through a resistor R. A voltage proportional to the current I is applied to the amplifier 7 via the resistor R, and its output is coupled to the pulse width modulator 8. The output signal of the pulse width modulator is a pulse width signal, that is, a square wave signal, and the load time ratio of the square wave pulse, that is, the width of the square wave pulse is modulated. The half bridge circuit is controlled by this pulse width signal. In this circuit, the power supply voltage U is applied via two switching elements 54 and 55 (for example, power MOSFETs) connected in series. The first switching element 54 is connected to the power supply potential. The second switching element 55 is connected to the reference potential. The input electrode of the piezoelectric transformer PT is connected to the potential point between the switching elements 54 and 55 through the induction element L that smoothes the output current.

  The pulse width signal controls one of the switching elements 54 and the inverted pulse width signal controls the other switching element 55, so that one of the switching elements 54, 55 is always in a conducting state. Conversely, the other is in a non-conductive state. When the first switching element 54 is in a conductive state, the power supply voltage U is applied to the potential point between the switching elements 54 and 55. When the second switching element 55 is in a conductive state, the reference potential is at a potential point between the switching elements 54 and 55.

  This control is stimulated as follows. When the piezoelectric transformer PT is excited at its series resonance frequency or parallel resonance frequency fs, a larger amount of current flows through the power amplifier. This adds a current through the parasitic input capacitance Cp. In an amplifier having a final stage transistor, significant power loss appears depending on the configuration size of the piezoelectric transformer PT in AB / B class operation.

  One possible remedy is the final stage operation in class D operation (switch mode). The transistors act as switches 54 and 55, and the inductive element L smoothes the output current.

  FIG. 5 is a schematic circuit diagram of a circuit device that performs input capacitance compensation based on the concept presented in FIG. This is an oscillator circuit for a piezoelectric transformer having a class D final stage (switch mode).

  Giving this circuit concept the external behavior of a linear amplifier is necessary for the start of oscillation, and for this, the pulse width modulator 8 is necessary with closed-loop control.

  Here, the operation of the last stage which operates with a clock having a constant current pulsation rate (Delta I) and an internal current closed loop control unit is recommended. The maximum control current can be limited within the closed loop control unit. Thereby, there is always an unconditional short-circuit tolerance at the output.

  The external voltage closed loop control unit sets a target value of current so that a desired voltage Ua is generated at the output of the amplifier.

  This type of circuit device is shown in FIG. The operating frequency of the D-stage final stage should be notably higher than the resonance frequency of the piezoelectric transformer PT. A coefficient of 10 or more is desirable.

  The capacitor Cv between the power supply potential and the reference potential is connected to the induction element L and functions as a memory for current passing through the piezoelectric transformer (Q = CU = it).

The circuit device includes a first branch circuit 1 having a series connection of a piezoelectric transformer PT and a first resistor R that functions as a shunt. The first branch circuit 1 is connected in parallel to a branch circuit 2 having a series connection of a capacitive element Ck and a second resistor Rk. A signal is detected between the component PT and the component R of each branch circuit 1, 2, or between the component Ck and the component Rk, and supplied to the differential amplifier 3. On the output side, the amplitude closed loop control unit 4 or the amplitude limiter is provided, and the output signal is applied to the first subtractor element 91. Similarly, in the first subtractor element 91, a target voltage detected according to the induction element L is applied. The subtractor element 91 prepares the difference between the two input signals on the output side. On the output side, this subtractor is connected to a closed loop control unit 10 which changes and in particular amplifies the signal difference in the subtractor 91. The resulting voltage is supplied via the limiter 4 to the second subtractor element 92 as a target value, where a voltage proportional to the current through the piezoelectric transformer PT is applied via the first resistor R. It is done. The resulting difference between the target value on the output side of the subtractor element 92 and the current value is coupled to the signal generator 8, which is connected in series as already described in FIG. Two switching elements 54 and 55 generate a pulse mode signal for controlling the half-bridge circuit.

This circuit device also has a feedback closed circuit I for closed-loop control of the voltage. Here, the excitation voltage and the output voltage subjected to amplitude closed-loop control in the differential amplifier are compared by the first subtractor element 91. The result is guided to the subtractor element 92. The second feedback closed circuit II for closed loop control of the current compares a value proportional to the target current with a voltage proportional to the current current via the shunt R, and according to the result, the piezoelectric transformer PT To control.

  The compensation concept described here can also be combined with other types of control circuits. It is only necessary to detect the variable of the piezoelectric transformer PT using the compensation branch unit 2 and the differential amplifier 3 and supply it to the control unit.

  Instead of a linear amplifier, it is also possible to use other types of amplifier styles, for example designs with switched closed-loop control amplifiers.

  It should also be noted that the features of these embodiments can be combined. Furthermore, this concept can be applied to other piezoelectric products.

PT Piezoelectric transformer R, Rk, Rs, R1, R2 Resistor Cp Input capacitance Ck, Cs, Cv Capacitance element L, Ls Inductive element 1, 2, Branch circuit 3, 5, 7, 100, 200 Amplifier 4 Amplitude closed loop control circuit 6 Series oscillation circuit 11, 12, 13, 21, 22, 23 Potential point 31, 32, 41, 51 Input 33, 42, 52 Output 54, 55 Switching element 91, 92 Subtractor element

Claims (10)

A first branch circuit (1) comprising a piezoelectric transformer (PT) having an input capacitance (Cp);
A second branch circuit (2) for compensating the input capacitance (Cp);
A differential amplifier (3) comprising a first input (31) coupled to the first branch circuit (1) and a second input (32) coupled to the second branch circuit (2); )When,
A voltage closed loop control circuit (I) and a current closed loop control circuit (II);
The first branch circuit (1) has a series connection of the piezoelectric transformer (PT) and a first resistor (R),
The second branch circuit (2) has a series connection of a capacitive element (Ck) and a second resistor (Rk),
The piezoelectric transformer (PT) is between the first potential point (11) and the second potential point (12) in the first branch circuit (1);
The first resistor (R) is between the second potential point (12) and the third potential point (13) in the first branch circuit (1);
The capacitive element (Ck) is between the first potential point (21) and the second potential point (22) in the second branch circuit (2);
The second resistor (Rk) is between the second potential point (22) and the third potential point (23) in the second branch circuit (2);
The second potential point (12) in the first branch circuit (1) is coupled to the first input (31) and the second potential in the second branch circuit (2); Point (22) is coupled to said second input (32),
The first potential point (11) in the first branch circuit (1) is coupled to the first potential point (21) in the second branch circuit (2), and the first potential point (11) The third potential point (13) in the branch circuit (1) is coupled to the third potential point (23) in the second branch circuit (2);
The signal output from the output (33) of the differential amplifier (3) is fed back to the voltage closed loop control circuit (I),
A signal proportional to the current through the piezoelectric transformer (PT) is fed back to the current closed loop control circuit (II).
Circuit device.   The time constant of the series connection of the capacitive element (Ck) of the second branch circuit (2) and the second resistor (Rk) is the same as the input capacitance (Cp) of the first branch circuit (1). The circuit device according to claim 1, wherein the time constant of the series connection with the first resistor (R) is equal to or substantially equal to the time constant.   In the equivalent circuit diagram of the piezoelectric transformer (PT) having a series oscillation circuit (6) including a capacitive element (Cs), an inductive element (Ls), and a resistor (Rs), the input capacitance (Cp) Corresponds to the capacitive element (Cp) connected in parallel to the series oscillation circuit (6).   The circuit device according to any one of claims 1 to 3, wherein an output (33) of the differential amplifier (3) is coupled to the piezoelectric transformer (PT) through a feedback branch circuit.   The circuit arrangement according to claim 4, wherein a feedback signal is applied to the first potential point (11, 21) of the first and second branch circuits (1, 2).   6. The circuit arrangement according to claim 4, wherein there is a further amplifier (5, 54, 55) in the feedback branch circuit.   The circuit device according to any one of claims 4 to 6, wherein an amplitude closed loop control unit (4) is provided in the feedback branch circuit.   The output (33) of the differential amplifier (3) passes through a pulse width modulator (8) and two switching elements (54, 55) connected in series between two potential points. The circuit device according to claim 4, wherein the circuit device is coupled to a piezoelectric transformer (PT). A method of controlling a piezoelectric transformer (PT) having an input capacitance (Cp) in a first branch circuit (1), the method comprising the first branch circuit (1) and the input capacitance (Cp) And detecting a voltage difference with the second branch circuit (2) that compensates) and feeding back to the piezoelectric transformer (PT) in a feedback closed circuit,
The first branch circuit (1) has a series connection of the piezoelectric transformer (PT) and a first resistor (R),
The second branch circuit (2) has a series connection of a capacitive element (Ck) and a second resistor (Rk),
The piezoelectric transformer (PT) is between the first potential point (11) and the second potential point (12) in the first branch circuit (1),
The first resistor (R) is between the second potential point (12) and the third potential point (13) in the first branch circuit (1),
The capacitive element (Ck) is between the first potential point (21) and the second potential point (22) in the second branch circuit (2),
The second resistor (Rk) is between the second potential point (22) and the third potential point (23) in the second branch circuit (2),
A first input (31) of the differential amplifier (3) is coupled to the second potential point of the first branch circuit (1), and a second input ( 32 ) of the differential amplifier (3) is Coupled to the second potential point of the second branch circuit ( 2 );
The first potential point (11) in the first branch circuit (1) is coupled to the first potential point (21) in the second branch circuit (2) and is connected to the first branch point. The third potential point (13) in the circuit (1) is coupled to the third potential point (23) in the second branch circuit (2);
The feedback closed circuit includes a voltage closed loop control circuit (I) and a current closed loop control circuit (II),
In the step of detecting the voltage difference, a voltage difference between the second potential point of the first branch circuit (1) and the second potential point of the second branch circuit ( 2 ) is detected,
In the feedback step, the signal output from the output (33) of the differential amplifier (3) is fed back to the voltage closed loop control circuit (I), and a signal proportional to the current passing through the piezoelectric transformer (PT) is obtained. The method is fed back to the current closed loop control circuit (II).   The time constant of the series connection between the capacitive element (Ck) of the second branch circuit (2) and the second resistor (Rk) is the input capacitance (Cp) of the first branch circuit (1). The method according to claim 9, wherein the time constant is equal to or approximately equal to the time constant of the series connection between the first resistor and the first resistor.

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